To facilitate installment of integrated circuit chips, the chips are typically packaged. The packaging provides leads for connecting chips to external devices and protection from environmental factors. For example, the packaging serves to protect the chip from exposure to contaminants, which could cause damage to the circuit components.
Packaging technology such as flip chip rely on bumps for interconnection between a chip and a substrate. The bumps may be formed by evaporation, by plating of solder, gold or copper, screening conductive paste or by forming ball bonds. A problem with the use of such bumps is that the interface between the bumps and the substrate or chip is vulnerable to failure during thermal cycling as a result of mechanical stress at the interface generated by differences in thermal expansion coefficients of the chip and the substrate. Thermal expansion may be caused by a number of factors including heat generated by the flow of electricity within the circuitry of the integrated circuit chip, environmental factors such as ambient temperature, and heating and cooling cycles caused by power on and off cycles of the chip.
To reduce temperature induced failure of integrated circuit chips, underfill has been used at the interface between the chip and the substrate.